The pseudotachylite from Champagnac in the Rochechouart meteorite crater, France.
Abstract
A vein system containing melt rock and hydrothermal crystallizations from the Champagnac quarry in the Rochechouart meteorite crater in France was characterized using petrographic and geochemical methods. The observed lack of characteristic shock phenomena in melt clasts, the angular shapes of clasts, and the structural field relations indicate that the melt fraction of the vein fillings represents pseudotachylite produced by friction during lateral shear movements. Bulk chemical analysis of vein fillings and defocused beam-electron probe results favor in situ formation of the melt and rule out the possibility that it represents injected impact melt. The following genetic process for the Champagnac pseudotachylite vein system is suggested: (1) the formation of clastic breccias by impact-induced lateral slip; (2) the sericitization of plagioclase of the breccia clasts and immediate host rocks by hydrothermal fluids circulating at high pressure; (3) the crystallization of hydrothermal phases and the development of pseudotachylite matrix and clast textures; and (4) long-term tectonic activity and additional hydrothermal modifications.
- Publication:
-
Journal of Geophysical Research
- Pub Date:
- March 1987
- DOI:
- 10.1029/JB092iB04p0E737
- Bibcode:
- 1987JGR....92E.737R
- Keywords:
-
- Geochemistry;
- Impact Melts;
- Meteorite Craters;
- Mineralogy;
- Petrology;
- Breccia;
- Chemical Composition;
- Electron Microscopy;
- Feldspars;
- France;
- Rubidium Isotopes;
- Strontium Isotopes;
- Meteorite Craters:Petrography